1. Field of the Invention
The present invention relates to a plunging constant velocity universal joint for the propeller shaft of an automobile.
A propeller shaft is used to transmit torque from a transmission to a differential gear set in a four-wheel drive (4WD) vehicle or a front-engine, rear-drive (FR) vehicle. While the use of 2-joint type propeller shafts is common, 3-joint type and 4-joint type are also used depending on the vehicle structure and specification requirements.
The constant velocity universal joints are roughly divided into fixed type that allows for only angular displacement between two shafts, and plunging type that allows for both angular displacement and axial displacement (plunging), that are selected and used according to the operating conditions, application and other factors. The present invention concerns with a double offset type constant velocity universal joint, among the plunging types, that is specifically designed for the propeller shaft of an automobile, and is reduced in weight and size.
2. Description of the Prior Art
Cardan joint (universal joint employing a cross spider) is predominantly used for the propeller shafts of 4DW vehicles and FR vehicles, except for some luxury models. However, non-uniformity of torque transmission characteristic of the Cardan joint leads to poor NVH (commonly known as noise, vibration and harshness) characteristics. Also the Cardan joint does not have a plunging mechanism, a slide spline (or serration) is required in the propeller shaft to absorb the geometrical changes generated by bounding of the vehicle or the like. However, since this portion has significantly large play and high sliding resistance, unusual vibration such as stick slip may be generated when vibration or sliding occurs during rotation. Thus it has been known that ride comfort of the vehicle is compromised for the passenger who is subjected to uncomfortable noise and/or vibration. Accordingly, constant velocity universal joints have been employed for the propeller shaft as means for improving the NVH characteristics.
In the automobile power-trains, there have been many examples of using constant velocity universal joints in the drive shafts, and majority of the constant velocity universal joints used in the propeller shafts have been those designed for the use in the drive shaft. However, when the operating conditions are compared between the propeller shafts and the drive shafts, the torque applied to a propeller shaft is about a half that of a drive shaft, and the practical range of the operating angles of the propeller shaft is narrower than that of the drive shaft. Thus use of a constant velocity universal joint designed for a drive shaft on a propeller shaft may be regarded as over specification compared to the specification requirements for the propeller shaft, with further improvements remaining to be done in terms of weight reduction, size reduction and cost cut-down. In addition, since the propeller shaft rotates at a higher speed than the drive shaft, the joint is desired to be more compact to facilitate high-speed rotation.